1. Technical Field
The present invention relates to imaging devices for measurement processing, and in particular, to an imaging device for measurement processing, which outputs a signal representing an image to perform an attribute measurement process defined in advance with respect to the imaged image.
2. Related Art
In the field of FA (Factory Automation) or the like, various types of image processing techniques have been used. In such image processing techniques, a visual sensor outputs a signal indicating an image to perform a measurement process on the shape, pattern, or color of a product to be manufactured, or a combination of the above (see Patent Document 1).
Indicators for the performance of such a visual sensor include installation distance (workpiece distance), (hereinafter also referred to as “WD”, “imaging target distance”) and detection range (hereinafter also referred to as “field”, “imaging range”). The installation distance is the distance between the visual sensor and the measuring target. The detection range is the range that can be imaged at the installation distance.
Users have various requirements concerning the combination of the WD and the field of the visual sensor. A great number of variations (product groups) are preferably lined up for the visual sensor to respond to such requests.
To this end, visual sensors provided with a lens having various combinations of WD and field may be lined up, or visual sensors in which the same lens is used but a back focus (hereinafter also referred to as “BF”) that is the distance from the lens to an imaging plane (e.g., of the imaging element) is varied may be lined up.
The value a of the WD and the value b of the BF are related by 1/a+1/b=1/f, where f is the focal distance of the lens according to the formula of the lens. Thus, various WD can be accommodated by varying the BF.
There are visual sensors in which the BF is fixed at the time of manufacturing and visual sensors in which the BF is adjustable by the user. In visual sensors in which the BF can be adjusted, a force cannot be directly applied to the lens along the axis on which the lens moves since the light from an object surface, which is the surface of the imaging target, enters the lens or the light enters the imaging plane of the imaging element from the lens along the axis on which the lens moves.
FIG. 10 is a first view illustrating an adjustment method of the back focus in a visual sensor. With reference to FIG. 10, in an adjustment method A, the force for moving the lens along an axis parallel to the axis of the lens movement is transmitted as a force for moving the lens along the axis on which the lens moves by an adjustment mechanism.
The force for moving the lens along the axis on which the lens moves thus can be indirectly applied on the lens. At the same time, however, the lens may not smoothly move on the axis since a moment about the axis orthogonal to the axis of the lens movement is exerted on the lens.
FIG. 11 is a second view illustrating an adjustment method of the back focus in a visual sensor. With reference to FIG. 11, in the adjustment method B, the force applied along a direction not parallel to the axis on which the lens moves (e.g., orthogonal direction) is transmitted as a force for moving the lens along the axis on which the lens moves by an adjustment mechanism.
According to the method B, the force for moving the lens along the axis on which the lens moves can be indirectly applied to the lens without exerting the moment that is exerted on the lens in the method A. Thus, the lens can be smoothly moved on the axis compared to the method A.